Transplantation of declined livers after normothermic perfusion

Donor-Related Risk Factors for Normothermic Machine Perfusion in Liver Transplantation: A Meta-Analysis

BACKGROUND AND AIMS

During normothermic machine perfusion (NMP), a variety of criteria are used to gauge the suitability of an organ for transplantation. However, the relations between donor factors and these criteria are poorly understood. The aim of this meta-analysis was to investigate the association between donor-related risk factors and the decision to transplant a liver subjected to NMP.

METHODS

A comprehensive literature search was performed for articles published up to March 2025 in four databases, reporting livers subjected to NMP for viability assessment prior to transplantation. Effect size (ES) was calculated using Cohen's D and log odds ratio.

RESULTS

Out of 806 unique articles, 18 were included in this meta-analysis, encompassing 690 liver grafts that underwent NMP. Following viability assessment during NMP, utilisation rate was 82% from donors after brain death and 68% from donors after circulatory death (ES: 0.08, p = 0.88). Transplanted livers had shorter cold ischemia time (ES: -0.34, p = 0.003) and lower liver weight (ES: -0.53, p < 0.001). Donor age, BMI and donor warm ischemia time did not differentiate between transplanted and unused groups. Differences were observed in viability assessment for lactate clearance (ES: 2.0, p = 0.005), glucose metabolism (ES: 2.2, p < 0.001), bile production (ES: 1.0, p = 0.003) and pH (ES: 1.9, p < 0.001). Excellent outcomes, including 10% non-anastomotic strictures, 89% graft survival and 93% patient survival, were achieved in a large cohort of high-risk livers.

CONCLUSION

Cold ischemia time and liver weight were identified as donor-related risk factors, whereas donor type, age and donor warm ischemia time appear not to impact the decision to transplant during NMP.

The Impact of Over Three Years Commercial Use of Ex Vivo Normothermic Machine Perfusion for Liver Transplantation in the USA: A UNOS/OPTN Database Analysis

BACKGROUND

Data to date using normothermic machine perfusion (NMP) devices to resuscitate and assess marginal livers such as donation after circulatory death (DCD) livers has shown impressive prevention of ischemic reperfusion injury and ischemic cholangiopathy (IC). We examined the impact of these NMP devices over 3 years after their release for commercial use on deceased donor liver transplantation (LT).

METHODS

We conducted a retrospective analysis of UNOS-SRTR data of livers recovered from DCD donors or older (≥ 60 years old) donation after brain death (DBD) donors for LT as well as the outcome of LT from DBD or DCD donors performed from 1/1/2016 to 6/30/2024 to compare differences with ischemic cold storage (ICS) versus NMP.

RESULTS

Among 10 778 donors of DCD livers, 1987 donors used NMP, and 8791 donors used ICS. In NMP group, the proportion of discarded livers was significantly less (7.25% vs. 30.52%), donors were older, donor BMI higher and more expanded criteria donor than those in ICS group (all, p < 0.001). For older donors, 416 cases used NMP and in 10 708 cases the liver was recovered via ICS. The discard rate of livers in NMP group was significantly less (4.33% vs. 12.18%, p < 0.001) and donors were older and donor BMI higher than that in ICS group. In DCD LT, the incidence of primary nonfunction (PNF), acute rejection within 1 year after LT as well as graft failure due to IC and hepatic artery thrombosis (HAT) in NMP group were significantly less than those in ICS group.

CONCLUSION

In conclusion, commercial use of NMP has expanded the donor pool by accelerated usage of marginal livers such as DCD and older donors by permitting longer preservation and functional assessment of the liver. In addition, the usage of NMP for DCD LTs was associate with a reduced incidence of rejection, PNF, graft failure due to IC and HAT.

The Impact of Liver Graft Preservation Method on Longitudinal Gut Microbiome Changes Following Liver Transplant: A Proof-of-concept Study

Background and Aims

End-stage liver disease is associated with disruptions in gut microbiota composition and function, which may facilitate gut-to-liver bacterial translocation, impacting liver graft integrity and clinical outcomes following liver transplantation. This study aimed to assess the impact of two liver graft preservation methods on fecal microbiota and changes in fecal and breath organic acids following liver transplantation.

Methods

This single-center, non-randomized prospective pilot study enrolled liver transplant patients whose grafts were preserved using either static cold storage or ex situ normothermic machine perfusion (NMP). Fresh stool and breath samples were collected immediately before surgery and at postoperative months 3, 6, and 12. Stool microbiota was profiled via 16S rRNA gene sequencing, stool short-chain fatty acids were measured using gas chromatography/-mass spectrometry, and breath volatile organic compounds (VOCs) were analyzed with selected-ion flow-tube mass spectrometry.

Results

Both cohorts experienced a loss of microbiota diversity and dominance by single taxa. The NMP cohort demonstrated enrichment of several beneficial gut taxa, while the static cold storage cohort showed depletion of such taxa. Various gut bacteria were found to correlate with stool short-chain fatty acids (e.g., lactic acid, butyric acid) and several VOCs.

Conclusions

Fecal microbiota alterations associated with end-stage liver disease do not fully normalize to a healthy control profile following liver transplantation. However, notable differences in microbiota composition and function were observed between liver graft preservation methods. Future research with larger randomized cohorts is needed to explore whether the NMP-associated shift in gut microbiota impacts clinical outcomes and if breath VOCs could serve as biomarkers of the clinical trajectory in liver transplant patients.

The impact of normothermic machine perfusion and acuity circles on waitlist time, mortality, and cost in liver transplantation: A multicenter experience

Ex situ normothermic machine perfusion (NMP) helps increase the use of extended criteria donor livers. However, the impact of an NMP program on waitlist times and mortality has not been evaluated. Adult patients listed for liver transplant (LT) at 2 academic centers from January 1, 2015, to September 1, 2023, were included (n=2773) to allow all patients ≥6 months follow-up from listing. Routine NMP was implemented on October 14, 2022. Waitlist outcomes were compared from pre-NMP pre-acuity circles (n=1460), pre-NMP with acuity circles (n=842), and with NMP (n=381). Median waitlist time was 79 days (IQR: 20-232 d) at baseline, 49 days (7-182) with acuity circles, and 14 days (5-56) with NMP ( p <0.001). The rate of transplant-per-100-person-years improved from 61-per-100-person-years to 99-per-100-person-years with acuity circles and 194-per-100-person-years with NMP ( p <0.001). Crude mortality without transplant decreased from 18.3% (n=268/1460) to 13.3% (n=112/843), to 6.3% (n=24/381) ( p <0.001) with NMP. The incidence of mortality without LT was 15-per-100-person-years before acuity circles, 19-per-100 with acuity circles, and 9-per-100-person-years after NMP ( p <0.001). Median Model for End-Stage Liver Disease at LT was lowest with NMP, but Model for End-Stage Liver Disease at listing was highest in this era ( p <0.0001). The median donor risk index of transplanted livers at baseline was 1.54 (1.27-1.82), 1.66 (1.42-2.16) with acuity circles, and 2.06 (1.63-2.46) with NMP ( p <0.001). Six-month post-LT survival was not different between eras ( p =0.322). The total cost of health care while waitlisted was lowest in the NMP era ($53,683 vs. $32,687 vs. $23,688, p <0.001); cost-per-day did not differ between eras ( p =0.152). The implementation of a routine NMP program was associated with reduced waitlist time and mortality without compromising short-term survival after liver transplant despite increased use of riskier grafts. Routine NMP use enables better waitlist management with reduced health care costs.

10 degree C static storage of porcine donation after circulatory death livers improves biliary viability and mitigates ischemia-reperfusion injury

Optimized static cold storage has the potential to improve the preservation of organs most vulnerable to ischemia-reperfusion injury. Data from lung transplantation suggest that storage at 10 °C improves mitochondrial preservation and subsequent allograft function compared with conventional storage on ice. Using a porcine model of donation after circulatory death, we compared static storage of livers at 10 °C to ice. Livers (N = 5 per group) underwent 10 hours of storage followed by 4 hours of normothermic machine perfusion (NMP) for real-time allograft assessment. Allografts were compared using established NMP viability criteria, tissue immunostaining, and tissue metabolomics. Livers stored at 10 °C demonstrated lower portal venous vascular resistance and greater hepatic artery vasoresponsiveness. Lactate clearance during NMP was similar between the groups. Livers stored at 10 °C showed favorable biochemical parameters of biliary viability, including greater bile volume, pH, and bicarbonate. Metabolomics analysis revealed increased aerobic respiration, improved electron transport chain function, and less DNA damage after reperfusion of livers stored at 10 °C. Static storage of donation after circulatory death livers with extended cold ischemic time at 10 °C demonstrates superior allograft function with evidence of improved biliary viability and mitochondrial function compared with ice. These data suggest that storage at 10 °C should be considered for translation to clinical practice.

Age Matters: What Affects the Cumulative Lifespan of a Transplanted Liver?

OBJECTIVE

To assess factors affecting the cumulative lifespan of a transplanted liver.

BACKGROUND

Liver aging is different from other solid organs. It is unknown how old a liver can actually get after liver transplantation.

METHODS

Deceased donor liver transplants from 1988 to 2021 were queried from the United States UNOS registry. Cumulative liver age was calculated as donor age + recipient graft survival.

RESULTS

In total, 184,515 livers were included. Most were donation after brain death donors (n = 175,343). The percentage of livers achieving >70, 80, 90, and 100 years cumulative age was 7.8% (n = 14,392), 1.9% (n = 3576), 0.3% (n = 528), and 0.01% (n = 21), respectively. The youngest donor age contributing to a cumulative liver age >90 years was 59 years, with posttransplant survival of 34 years. In pediatric recipients, 736 (4.4%) and 282 livers (1.7%) survived >50 and 60 years overall, respectively. Transplanted livers achieved cumulative age >90 years in 2.86 per 1000 and >100 years in 0.1 per 1000. The U.S. population at large has a cumulative "liver age" >90 years in 5.35 per 1000 persons, and >100 years in 0.2 per 1000. Livers aged >60 years at transplant experienced both improved cumulative survival ( P < 0.0001) and interestingly improved survival after transplantation ( P < 0.0001). Recipient warm ischemia time of >30 minutes was most predictive of reduced cumulative liver survival overall (n = 184,515, hazard ratio = 1.126, P < 0.001) and excluding patients with mortality in the first 6 months (n = 151,884, hazard ratio = 0.973, P < 0.001).

CONCLUSIONS

In summary, transplanted livers frequently get as old as those in the average population despite ischemic-reperfusion-injury and immunosuppression. The presented results justify using older donor livers regardless of donation type, even in sicker recipients with limited options.

Viability Assessment During Normothermic Machine Liver Perfusion: A Literature Review

BACKGROUND AND OBJECTIVE

The discrepancy between donor organ availability and demand leads to a significant waiting-list dropout rate and mortality. Although quantitative tools such as the Donor Risk Index (DRI) help assess organ suitability, many potentially viable organs are still discarded due to the lack of universally accepted markers to predict post-transplant outcomes. Normothermic machine perfusion (NMP) offers a platform to assess viability before transplantation. Thus, livers considered unsuitable for transplantation based on the DRI can be evaluated and potentially transplanted. During NMP, various viability criteria have been proposed. These criteria are neither homogeneous nor consensual. In this review, we aimed to describe the viability criteria during NMP and evaluate their ability to predict hepatic graft function following transplantation. We conducted a PubMed search using the terms 'liver transplantation', 'normothermic machine perfusion' and 'assessment', including only English publications up to February 2024. Viability assessment during NMP includes multiple hepatocellular and cholangiocellular criteria. Lactate clearance and bile production are commonly used indicators, but their ability to predict post-transplant outcomes varies significantly. The predictive value of cholangiocellular criteria such as bile pH, bicarbonate and glucose levels remains under investigation. Novel markers, such as microRNAs and proteomic profiles, offer the potential to enhance graft evaluation accuracy and provide insights into the molecular mechanisms underlying liver viability. Combining perfusion parameters with biomarkers may improve the prediction of long-term graft survival. Future research should focus on standardising viability assessment protocols and exploring real-time biomarker evaluations, which could enhance transplantation outcomes and expand the donor pool.

The Potential Utilization of Machine Perfusion to Increase Transplantation of Macrosteatotic Livers

BACKGROUND

The demand for liver transplantation has led to the utilization of marginal grafts including moderately macrosteatotic livers (macrosteatosis ≥30% [Mas30]), which are associated with an elevated risk of graft failure. Machine perfusion (MP) has emerged as a technique for organ preservation and viability testing; however, little is known about MP in Mas30 livers. This study evaluates the utilization and outcomes of Mas30 livers in the era of MP.

METHODS

The Organ Procurement and Transplantation Network database was queried to identify biopsy-proven Mas30 deceased donor liver grafts between June 1, 2016, and June 23, 2023. Univariable and multivariable models were constructed to study the association between MP and graft utilization and survival.

RESULTS

The final cohort with 3317 Mas30 livers was identified, of which 72 underwent MP and were compared with 3245 non-MP livers. Among Mas30 livers, 62 (MP) and 1832 (non-MP) were transplanted (utilization of 86.1% versus 56.4%, P  < 0.001). Donor and recipient characteristics were comparable between MP and non-MP groups. In adjusted analyses, MP was associated with significantly increased Mas30 graft utilization (odds ratio, 7.89; 95% confidence interval [CI], 3.76-16.58; P  < 0.001). In log-rank tests, MP was not associated with 1- and 3-y graft failure (hazard ratio, 0.49; 95% CI, 0.12-1.99; P  = 0.319 and hazard ratio 0.43; 95% CI, 0.11-1.73; P  = 0.235, respectively).

CONCLUSIONS

The utilization rate of Mas30 grafts increases with MP without detriment to graft survival. This early experience may have implications for increasing the available donor pool of Mas30 livers.

Changing Landscape of Open Offers in Liver Transplantation in the Machine Perfusion Era: Exposure, Equity, and Economics

BACKGROUND

Open offers (OOs) in liver transplantation (LT) result from bypassing the traditional allocation system. Little is known about the trends of OOs or the differences in donor/recipient characteristics compared to traditionally placed organs. We aim to quantify modern practices regarding OOs and understand NMP's impact, focusing on social determinants of health (SDH), cost, and graft-associated risk.

METHODS

LTs from 1/1/2018 to 12/31/2023 at a single center were included. NMP was implemented on 10/1/2022. The CDC (centers for disease control)-validated social vulnerability index (SVI) and donor risk index (DRI) were calculated. Comprehensive complications index (CCI), Clavien-Dindo grades, patient and graft survival, and costs of transplantation were included.

RESULTS

1162 LTs were performed; 193 (16.8%) from OOs. OOs were more common in the post-NMP era (26.5% vs. 13.3%, p < 0.001). Pre-NMP, patients receiving OOs had longer waitlist times (118 vs. 69 days, p < 0.001), lower MELDs (17 vs. 25 points, p < 0.001), and riskier grafts (DRI = 1.8 vs. 1.6, p = 0.004) compared to standard offers. Post-NMP, recipients receiving OOs demonstrated no difference in waitlist time (27 vs. 20 days, p = 0.21) or graft risk (DRI = 2.03 vs. 2.23, p = 0.17). OO recipient MELD remained lower (16 vs. 22, p < 0.001). OO recipients were more socially vulnerable (SVI), pre-NMP (0.41 vs. 0.36, p = 0.004), but less vulnerable after NMP (0.23 vs. 0.36, p = 0.019). Despite increased graft risk, pre-NMP OO-LTs were less expensive in the 90-day global period ($154 939 vs. $178 970, p = 0.002) and the 180-days pre-/post-LT ($208 807 vs. $228 091, p = 0.021). Cost trends remained similar with NMP.

CONCLUSION

OOs are increasingly utilized and may be appealing due to demonstrated cost reductions even with NMP. Although most OO-related metrics in our center remain similar before and after machine perfusion, programs should take caution that increasing use does not worsen organ access for socially vulnerable populations.

Liver machine perfusion technology: Expanding the donor pool to improve access to liver transplantation

The imbalance between organ supply and demand continues to limit the broader benefits of organ transplantation. Machine perfusion (MP) may increase the supply of donor livers by expanding the use of extended-criteria donors. Using the United Network for Organ Sharing/Organ Procurement and Transplantation Network and the Standard Transplant Analysis and Research dataset, we reviewed the effect of MP implementation on the behavior of transplant centers. We identified 15 high-utilizing MP centers that were matched to suitable controls based on volume and geographical proximity. We conducted a differences-in-differences analysis using linear regression to estimate the impact of MP adoption on the transplant centers' donor utilization. We found a significant increase in cold ischemia time and organs with donor warm ischemia time over 30 minutes (P < .05). After removing one outlier center, the analysis showed that these centers through MP accepted overall more donation after circulatory death donors, donation after circulatory death donors over 50 years old, donors with macrovesicular steatosis greater than 30% on liver biopsy, and donor warm ischemia time over 30 minutes (P < .05). MP has allowed centers to expand their use of extended-criteria donors beyond traditional cutoffs and to increase patient access to liver transplantation.

Safety and use of late-turndown liver allografts to increase rate of transplantation

BACKGROUND

The demand for liver transplants (LT) in the United States far surpasses the availability of allografts. New allocation schemes have resulted in occasional difficulties with allograft placement and increased intraoperative turndowns. We aimed to evaluate the outcomes related to use of late-turndown liver allografts.

METHODS

A review of prospectively collected data of LTs at a single center from July 2019 to July 2023 was performed. Late-turndown placement was defined as an open offer 6 h prior to donation, intraoperative turndown by primary center, or post-cross-clamp turndown.

RESULTS

Of 565 LTs, 25.1% (n = 142) received a late-turndown liver allograft. There were no significant differences in recipient age, gender, BMI, or race (all p > 0.05), but MELD was lower for the late-turndown LT recipient group (median 15 vs 21, p < 0.001). No difference in 30-day, 6-month, or 1-year survival was noted on logistic regression, and no difference in patient or graft survival was noted on Cox proportional hazard regression. Late-turndown utilization increased during the study from 17.2% to 25.8%, and median waitlist time decreased from 77 days in 2019 to 18 days in 2023 (p < 0.001).

CONCLUSION

Use of late-turndown livers has increased and can increase transplant rates without compromising post-transplant outcomes with appropriate selection.

Impact of Back-to-Base Normothermic Machine Perfusion on Complications and Costs: A Multicenter, Real-World Risk-Matched Analysis

OBJECTIVE

Assess cost and complication outcomes after liver transplantation (LT) using normothermic machine perfusion (NMP).

BACKGROUND

End-ischemic NMP is often used to aid logistics, yet its impact on outcomes after LT remains unclear, as does its true impact on costs associated with transplantation.

METHODS

Deceased donor liver recipients at 2 centers (January 1, 2019, to June 30, 2023) were included. Retransplants, splits, and combined grafts were excluded. End-ischemic NMP (OrganOx-Metra) was implemented in October 2022 for extended-criteria donation after brain death (DBDs), all donations after circulatory deaths (DCDs), and logistics. NMP cases were matched 1:2 with static cold storage controls (SCS) using the Balance-of-Risk [donation after brain death (DBD)-grafts] and UK-DCD Score (DCD-grafts).

RESULTS

Overall, 803 transplantations were included, 174 (21.7%) receiving NMP. Matching was achieved between 118 NMP-DBDs with 236 SCS; and 37 NMP-DCD with 74 corresponding SCS. For both graft types, median inpatient comprehensive complications index values were comparable between groups. DCD-NMP grafts experienced reduced cumulative 90-day comprehensive complications index (27.6 vs 41.9, P =0.028). NMP also reduced the need for early relaparotomy and renal replacement therapy, with subsequently less frequent major complications (Clavien-Dindo ≥IVa). This effect was more pronounced in DCD transplants. NMP had no protective effect on early biliary complications. Organ acquisition/preservation costs were higher with NMP, yet NMP-treated grafts had lower 90-day pretransplant costs in the context of shorter waiting list times. Overall costs were comparable for both cohorts.

CONCLUSIONS

This is the first risk-adjusted outcome and cost analysis comparing NMP and SCS. In addition to logistical benefits, NMP was associated with a reduction in relaparotomy and bleeding in DBD grafts, and overall complications and post-LT renal replacement for DCDs. While organ acquisition/preservation was more costly with NMP, overall 90-day health care costs-per-transplantation were comparable.

[Machine perfusion in transplantation surgery]

The use of machine perfusion in solid organ transplantation has developed tremendously worldwide in recent years. Although the number of randomized controlled trials in the field of organ preservation is still limited, machine perfusion has been shown to be superior to static cold storage of donor organs. Various devices for clinical use with hypothermia or normothermia are already available for most organs. Whether and which perfusion strategy is superior to the others is the subject of current clinical research. This also applies to the further evaluation of possible synergistic effects in the sequential use of the various protocols. The common goal of all dynamic perfusion technologies is to optimize organ preservation between removal and transplantation. By testing the quality of marginal donor organs prior to transplantation, it should also be possible to use these organs without exposing the patient to increased risk. This can lead to a significant expansion of the donor pool. This is particularly important in Germany, where there is an ongoing shortage of organs and restrictive legislation regarding the expansion of the donor pool. Furthermore, the perfusion technology offers the possibility to serve as a platform for other ex situ and in situ therapies on isolated organs. In addition to the conditioning of pre-damaged organs for transplantation, this could lead to further applications in the context of targeted organ therapies and also to improved transplant logistics in the future.

Viability assessment of the liver during ex-situ machine perfusion prior to transplantation

PURPOSE OF REVIEW

In an attempt to reduce waiting list mortality in liver transplantation, less-than-ideal quality donor livers from extended criteria donors are increasingly accepted. Predicting the outcome of these organs remains a challenge. Machine perfusion provides the unique possibility to assess donor liver viability pretransplantation and predict postreperfusion organ function.

RECENT FINDINGS

Assessing liver viability during hypothermic machine perfusion remains challenging, as the liver is not metabolically active. Nevertheless, the levels of flavin mononucleotide, transaminases, lactate dehydrogenase, glucose and pH in the perfusate have proven to be predictors of liver viability. During normothermic machine perfusion, the liver is metabolically active and in addition to the perfusate levels of pH, transaminases, glucose and lactate, the production of bile is a crucial criterion for hepatocyte viability. Cholangiocyte viability can be determined by analyzing bile composition. The differences between perfusate and bile levels of pH, bicarbonate and glucose are good predictors of freedom from ischemic cholangiopathy.

SUMMARY

Although consensus is lacking regarding precise cut-off values during machine perfusion, there is general consensus on the importance of evaluating both hepatocyte and cholangiocyte compartments. The challenge is to reach consensus for increased organ utilization, while at the same time pushing the boundaries by expanding the possibilities for viability testing.

Preclinical validation of a customized circuit for ex situ uninterrupted cold-to-warm prolonged perfusion of the liver

CONTEXT

Clinical adoption of ex situ liver perfusion is growing. While hypothermic perfusion protects against ischemia-reperfusion injury in marginal grafts, normothermic perfusion enables organ viability assessment and therefore selection of borderline grafts. The combination of hypothermic and normothermic perfusion, known as "cold-to-warm," may be the optimal sequence for organ preservation, but is difficult to achieve with most commercial perfusion systems. We developed an adaptable customized circuit allowing uninterrupted "cold-to-warm" perfusion and conducted preclinical studies on healthy porcine livers and discarded human livers to demonstrate the circuit's efficacy.

METHODS

In collaboration with bioengineers, we developed a customized circuit that adapts to extracorporeal circulation consoles used in cardiovascular surgery and includes a proprietary reservoir enabling easy perfusate change without interrupting perfusion. This preclinical study was conducted on porcine and human livers. Perfusion parameters (pressures, flows, oxygenation) and organ viability were monitored.

RESULTS

The customized circuit was adapted to a LivaNova S5® console, and the perfusions were flow-driven with real-time pressure monitoring. Ten porcine liver and 12 discarded human liver perfusions were performed during 14 to 18 h and 7 to 25 h, respectively. No hyperpressure was observed (porcine and human portal pressure 2-6 and 2-8 mm Hg; arterial pressure 10-65 and 20-65 mm Hg, respectively). No severe histological tissue injury was observed (Suzuki score ≤ 3 at the end of perfusion). Seven (70%) porcine livers and five (42%) human livers met the UK viability criteria.

CONCLUSION

The customized circuit and system design enables smooth uninterrupted "cold-to-warm" perfusion not present in current commercial perfusion systems.

Machine perfusion in liver transplantation: recent advances and coming challenges

PURPOSE OF REVIEW

Machine perfusion has been adopted into clinical practice in Europe since the mid-2010s and, more recently, in the United States (US) following approval of normothermic machine perfusion (NMP). We aim to review recent advances, provide discussion of potential future directions, and summarize challenges currently facing the field.

RECENT FINDINGS

Both NMP and hypothermic-oxygenated perfusion (HOPE) improve overall outcomes after liver transplantation versus traditional static cold storage (SCS) and offer improved logistical flexibility. HOPE offers additional protection to the biliary system stemming from its' protection of mitochondria and lessening of ischemia-reperfusion injury. Normothermic regional perfusion (NRP) is touted to offer similar protective effects on the biliary system, though this has not been studied prospectively.The most critical question remaining is the optimal use cases for each of the three techniques (NMP, HOPE, and NRP), particularly as HOPE and NRP become more available in the US. There are additional questions regarding the most effective criteria for viability assessment and the true economic impact of these techniques. Finally, with each technique purported to allow well tolerated use of riskier grafts, there is an urgent need to define terminology for graft risk, as baseline population differences make comparison of current data challenging.

SUMMARY

Machine perfusion is now widely available in all western countries and has become an essential tool in liver transplantation. Identification of the ideal technique for each graft, optimization of viability assessment, cost-effectiveness analyses, and proper definition of graft risk are the next steps to maximizing the utility of these powerful tools.

Return of the cold: How hypothermic oxygenated machine perfusion is changing liver transplantation

Hypothermic Oxygenated machine PErfusion (HOPE) has recently emerged as a preservation technique which can reduce ischemic injury and improve clinical outcomes following liver transplantation. First developed with the advent solid organ transplantation techniques, hypothermic machine perfusion largely fell out of favour following the development of preservation solutions which can satisfactorily preserve grafts using the cheap and simple method, static cold storage (SCS). However, with an increasing need to develop techniques to reduce graft injury and better utilise marginal and donation after circulatory death (DCD) grafts, HOPE has emerged as a relatively simple and safe technique to optimise clinical outcomes following liver transplantation. Perfusing the graft with cold, acellular, oxygenated perfusate either via the portal vein (PV) alone, or via both the PV and hepatic artery (HA), HOPE is generally commenced for a period of 1-2 h immediately prior to implantation. The technique has been validated by multiple randomised control trials, and pre-clinical evidence suggests HOPE primarily reduces graft injury by decreasing the accumulation of harmful mitochondrial intermediates, and subsequently, the severity of post-reperfusion injury. HOPE can also facilitate real time graft assessment, most notably via the measurement of flavin mononucleotide (FMN) in the perfusate, allowing transplant teams to make better informed clinical decisions prior to transplantation. HOPE may also provide a platform to administer novel therapeutic agents to ex situ organs without risk of systemic side effects. As such, HOPE is uniquely positioned to revolutionise how liver transplantation is approached and facilitate optimised clinical outcomes for liver transplant recipients.

Normothermic machine perfusion for liver transplantation: current state and future directions

PURPOSE OF REVIEW

The number of patients on the liver transplant waitlist continues to grow and far exceeds the number of livers available for transplantation. Normothermic machine perfusion (NMP) allows for ex-vivo perfusion under physiologic conditions with the potential to significantly increase organ yield and expand the donor pool.

RECENT FINDINGS

Several studies have found increased utilization of donation after cardiac death and extended criteria brain-dead donor livers with implementation of NMP, largely due to the ability to perform viability testing during machine perfusion. Recently, proposed viability criteria include lactate clearance, maintenance of perfusate pH more than 7.2, ALT less than 6000 u/l, evidence of glucose metabolism and bile production. Optimization of liver grafts during NMP is an active area of research and includes interventions for defatting steatotic livers, preventing ischemic cholangiopathy and rejection, and minimizing ischemia reperfusion injury.

SUMMARY

NMP has resulted in increased organ utilization from marginal donors with acceptable outcomes. The added flexibility of prolonged organ storage times has the potential to improve time constraints and transplant logistics. Further research to determine ideal viability criteria and investigate ways to optimize marginal and otherwise nontransplantable liver grafts during NMP is warranted.

Current Techniques and Indications for Machine Perfusion and Regional Perfusion in Deceased Donor Liver Transplantation

Since the advent of University of Wisconsin preservation solution in the 1980s, clinicians have learned to work within its confines. While affording improved outcomes, considerable limitations still exist and contribute to the large number of livers that go unused each year, often for fear they may never work. The last 10 years have seen the widespread availability of new perfusion modalities which provide an opportunity for assessing organ viability and prolonged organ storage. This review will discuss the role of in situ normothermic regional perfusion for livers donated after circulatory death. It will also describe the different modalities of ex situ perfusion, both normothermic and hypothermic, and discuss how they are thought to work and the opportunities afforded by them.

Continuous Renal Replacement Therapy During Long-term Normothermic Machine Perfusion of Human Donor Livers for up to 7 D

Background

Normothermic machine perfusion (NMP) is used to preserve and test donor livers before transplantation. During NMP, the liver is metabolically active and produces waste products, which are released into the perfusate. In this study, we describe our simplified and inexpensive setup that integrates continuous renal replacement therapy (CRRT) with NMP for up to 7 d. We also investigated if the ultrafiltrate could be used for monitoring perfusate concentrations of small molecules such as glucose and lactate.

Methods

Perfusate composition (urea, osmolarity, sodium, potassium, chloride, calcium, magnesium, phosphate, glucose, and lactate) was analyzed from 56 human NMP procedures without CRRT. Next, in 6 discarded human donor livers, CRRT was performed during NMP by integrating a small dialysis filter (0.2 m2) into the circuit to achieve continuous ultrafiltration combined with continuous fluid substitution for up to 7 d.

Results

Within a few hours of NMP without CRRT, a linear increase in osmolarity and concentrations of urea and phosphate to supraphysiological levels was observed. After integration of CRRT into the NMP circuit, the composition of the perfusate was corrected to physiological values within 12 h, and this homeostasis was maintained during NMP for up to 7 d. Glucose and lactate levels, as measured in the CRRT ultrafiltrate, were strongly correlated with perfusate levels (r = 0.997, P < 0.001 and r = 0.999, P < 0.001, respectively).

Conclusions

The integration of CRRT into the NMP system corrected the composition of the perfusate to near-physiological values, which could be maintained for up to 7 d. The ultrafiltrate can serve as an alternative to the perfusate to monitor concentrations of small molecules without potentially compromising sterility.

Normothermic Machine Perfusion Systems: Where Do We Go From Here?

Normothermic machine perfusion (NMP) aims to preserve organs ex vivo by simulating physiological conditions such as body temperature. Recent advancements in NMP system design have prompted the development of clinically effective devices for liver, heart, lung, and kidney transplantation that preserve organs for several hours/up to 1 d. In preclinical studies, adjustments to circuit structure, perfusate composition, and automatic supervision have extended perfusion times up to 1 wk of preservation. Emerging NMP platforms for ex vivo preservation of the pancreas, intestine, uterus, ovary, and vascularized composite allografts represent exciting prospects. Thus, NMP may become a valuable tool in transplantation and provide significant advantages to biomedical research. This review recaps recent NMP research, including discussions of devices in clinical trials, innovative preclinical systems for extended preservation, and platforms developed for other organs. We will also discuss NMP strategies using a global approach while focusing on technical specifications and preservation times.

Discarded livers tested by normothermic machine perfusion in the VITTAL trial: Secondary end points and 5-year outcomes

Normothermic machine perfusion (NMP) enables pretransplant assessment of high-risk donor livers. The VITTAL trial demonstrated that 71% of the currently discarded organs could be transplanted with 100% 90-day patient and graft survivals. Here, we report secondary end points and 5-year outcomes of this prospective, open-label, phase 2 adaptive single-arm study. The patient and graft survivals at 60 months were 82% and 72%, respectively. Four patients lost their graft due to nonanastomotic biliary strictures, one caused by hepatic artery thrombosis in a liver donated following brain death, and 3 in elderly livers donated after circulatory death (DCD), which all clinically manifested within 6 months after transplantation. There were no late graft losses for other reasons. All the 4 patients who died during the study follow-up had functioning grafts. Nonanastomotic biliary strictures developed in donated after circulatory death livers that failed to produce bile with pH >7.65 and bicarbonate levels >25 mmol/L. Histological assessment in these livers revealed high bile duct injury scores characterized by arterial medial necrosis. The quality of life at 6 months significantly improved in all but 4 patients suffering from nonanastomotic biliary strictures. This first report of long-term outcomes of high-risk livers assessed by normothermic machine perfusion demonstrated excellent 5-year survival without adverse effects in all organs functioning beyond 1 year (ClinicalTrials.gov number NCT02740608).

Screening for mitochondrial function before use-routine liver assessment during hypothermic oxygenated perfusion impacts liver utilization

BACKGROUND

To report on a concept of liver assessment during ex situ hypothermic oxygenated perfusion (HOPE) and its significant impact on liver utilization.

METHODS

An analysis of prospectively collected data on donation after circulatory death (DCD) livers, treated by HOPE at our institution, during a 11-year period between January 2012 and December 2022.

FINDINGS

Four hundred and fifteen DCD Maastricht III livers were offered during the study period in Switzerland, resulting in 249 liver transplants. Of those, we performed 158 DCD III liver transplants at our institution, with 1-year patient survival and death censored graft survival (death with functioning graft) of 87 and 89%, respectively, thus comparable to benchmark graft survivals of ideal DBD and DCD liver transplants (89% and 86%). Correspondingly, graft loss for primary non-function or cholangiopathy was overall low, i.e., 7/158 (4.4%) and 11/158 (6.9%), despite more than 82% of DCD liver grafts ranked high (6-10 points) or futile risk (>10 points) according to the UK-DCD score. Consistently, death censored graft survival was not different between low-, high-risk or futile DCD III livers. The key behind these achievements was the careful development and implementation of a routine perfusate assessment of mitochondrial biomarkers for injury and function, i.e., release of flavin mononucleotide from complex I, perfusate NADH, and mitochondrial CO2 production during HOPE, allowing a more objective interpretation of liver quality on a subcellular level, compared to donor derived data.

INTERPRETATION

HOPE after cold storage is a highly suitable and easy to perform perfusion approach, which allows reliable liver graft assessment, enabling surgeons to make a fact based decision on whether or not to implant the organ. HOPE-treatment should be combined with viability assessment particularly when used for high-risk organs, including DCD livers or organs with relevant steatosis.

FUNDING

This study was supported by the Swiss National Foundation (SNF) grant 320030_189055/1 to PD.

Bile proteome reveals biliary regeneration during normothermic preservation of human donor livers

Normothermic machine perfusion (NMP) after static cold storage is increasingly used for preservation and assessment of human donor livers prior to transplantation. Biliary viability assessment during NMP reduces the risk of post-transplant biliary complications. However, understanding of molecular changes in the biliary system during NMP remains incomplete. We performed an in-depth, unbiased proteomics analysis of bile collected during sequential hypothermic machine perfusion, rewarming and NMP of 55 human donor livers. Longitudinal analysis during NMP reveals proteins reflective of cellular damage at early stages, followed by upregulation of secretory and immune response processes. Livers with bile chemistry acceptable for transplantation reveal protein patterns implicated in regenerative processes, including cellular proliferation, compared to livers with inadequate bile chemistry. These findings are reinforced by detection of regenerative gene transcripts in liver tissue before machine perfusion. Our comprehensive bile proteomics and liver transcriptomics data sets provide the potential to further evaluate molecular mechanisms during NMP and refine viability assessment criteria.

Impact of Portable Normothermic Machine Perfusion for Liver Transplantation From Adult Deceased Donors

OBJECTIVE

To assess how liver allografts preserved using portable normothermic machine perfusion (NMP) compare against those that underwent ischemic cold storage (ICS) in the setting of donation after brain death (DBD) and donation after circulatory death (DCD) liver transplantation (LT).

BACKGROUND

Compared with conventional ICS, NMP may offer more homeostatic preservation, permit physiological assessment of organ function, and provide opportunities for graft improvement/modification. We report a single-center US experience of liver NMP.

METHODS

A single-center, retrospective analysis of collected data on 541 adult whole LTs from 469 DBD donors [NMP (n = 58) vs ICS (n = 411)] and 72 DCD donors [NMP (n = 52) vs ICS (n = 20)] between January 2016 and December 2022.

RESULTS

In DBD LT, male sex [odds ratio (95% CI): 1.83 (1.08-3.09)] and >10% macrosteatosis of the donor liver [1.85 (1.10-3.10)] were statistically significant independent risk factors of early allograft dysfunction (EAD). Donor age >40 years and cold ischemia time >7 hours were independent risk factors of reperfusion syndrome (RPS). One-year, 3-year, and 5-year incidences of ischemic cholangiopathy (IC) did not differ significantly in DBD cases between the NMP and ICS cohorts. In DCD LT, NMP was an independent protective factor against EAD [0.11 (0.03-0.46)] and RPS [0.04 (0.01-0.25)]. The incidence of IC in the DCD cases at 1-year and 3-year time points was significantly lower in the NMP cohort (1.9% compared with 20% in the ICS group).

CONCLUSIONS

Compared with conventional ICS, NMP can significantly reduce the incidence of EAD, RPS, and IC after DCD LT.

Defatting of Human Livers During Long-Term e x situ Normothermic Perfusion: Novel Strategy to Rescue Discarded Organs for Transplantation

OBJECTIVE

To develop a protocol for the defatting of steatotic liver grafts during long-term ex situ normothermic machine perfusion.

BACKGROUND

Despite the alarming increase in donor organ shortage, the highly prevalent fatty liver grafts are often discarded due to the risk of primary nonfunction. Effective strategies preventing such outcomes are currently lacking. An exciting new avenue is the introduction of ex situ normothermic machine perfusion (NMP), enabling a liver to remain fully functional for up to 2 weeks and providing a unique window of opportunity for defatting before transplantation.

METHODS

Over a 5-year period, 23 discarded liver grafts and 28 partial livers from our resection program were tested during ex situ normothermic machine perfusion. The steatosis degree was determined on serial biopsies by expert pathologists, and triglyceride contents were measured simultaneously.

RESULTS

Of 51 liver grafts, 20 were steatotic, with up to 85% macrovesicular steatosis, and were perfused for up to 12 days. Ten livers displayed marked (5 of which almost complete) loss of fat, while the other 10 did not respond to long-term perfusion. Successful defatting was related to prolonged perfusion, automated glucose control, circadian nutrition, and L-carnitine/fenofibrate supplementation. Pseudopeliotic steatosis and the associated activation of Kupffer/stellate cells were unexpected processes that might contribute to defatting. Synthetic and metabolic functions remained preserved for most grafts until perfusion ended.

CONCLUSION

Ex situ long-term perfusion effectively reduces steatosis while preserving organ viability and may in the future allow transplantation of primarily unusable high-risk grafts, significantly increasing the number of organs available for transplantation.

Real-world implementation of normothermic machine perfusion: A detailed analysis of intraoperative and early postoperative impact

BACKGROUND

Outcome data for the great majority of liver normothermic machine perfusion (NMP) cases derive from the strict confines of clinical trials. Detailed specifics regarding the intraoperative and early postoperative impact of NMP on reperfusion injury and its sequelae during real-world use of this emerging technology remain largely unavailable.

METHODS

We analyzed transplants performed in a 3-month pilot period during which surgeons invoked commercial NMP at their discretion. Living donor, multi-organ, and hypothermic machine perfusion transplants were excluded.

RESULTS

Intraoperatively, NMP (n = 24) compared to static cold storage (n = 25) recipients required less peri-reperfusion bolus epinephrine (0 vs. 60 μg; p < .001) and post-reperfusion fresh frozen plasma (2.5 vs. 7.0 units; p = .0069), platelets (.0 vs. 2.0 units; p = .042), and hemostatic agents (0% vs. 24%; p = .010). Time from incision to venous reperfusion did not differ (3.6 vs. 3.1; p = .095) but time from venous reperfusion to surgery end was shorter for NMP recipients (2.3 vs. 2.8 h; p = .0045). Postoperatively, NMP recipients required fewer red blood cell (1.0 vs. 4.0 units; p = .0083) and fresh frozen plasma (4.0 vs. 7.0 units; p = .046) transfusions, had shorter intensive care unit stays (33.5 vs. 58.4 h; p = .012), and experienced less early allograft dysfunction according to both the Model for Early Allograft Function Score (3.4 vs. 5.0; p = .0047) and peak AST within 10 days of transplant (619 vs. 1,181 U/L; p = .036). Liver acceptance for the corresponding recipient was conditional on NMP use for 63% (15/24) of cases.

CONCLUSION

Real-world NMP use was associated with significantly lower intensity of reperfusion injury and intraoperative and postoperative care that may translate into patient benefit.

How to Preserve Steatotic Liver Grafts for Transplantation

Liver allograft steatosis is a significant risk factor for postoperative graft dysfunction and has been associated with inferior patient and graft survival, particularly in the case of moderate or severe macrovesicular steatosis. In recent years, the increasing incidence of obesity and fatty liver disease in the population has led to a higher proportion of steatotic liver grafts being used for transplantation, making the optimization of their preservation an urgent necessity. This review discusses the mechanisms behind the increased susceptibility of fatty livers to ischemia-reperfusion injury and provides an overview of the available strategies to improve their utilization for transplantation, with a focus on preclinical and clinical evidence supporting donor interventions, novel preservation solutions, and machine perfusion techniques.

Normothermic Ex Vivo Machine Perfusion for Liver Transplantation: A Systematic Review of Progress in Humans

BACKGROUND

Liver transplantation is a lifesaving procedure for patients with end-stage liver disease (ESLD). However, many patients never receive a transplant due to insufficient donor supply. Historically, organs have been preserved using static cold storage (SCS). However, recently, ex vivo normothermic machine perfusion (NMP) has emerged as an alternative technique. This paper aims to investigate the clinical progress of NMP in humans.

METHODS

Papers evaluating the clinical outcomes of NMP for liver transplantation in humans were included. Lab-based studies, case reports, and papers utilizing animal models were excluded. Literature searches of MEDLINE and SCOPUS were conducted. The revised Cochrane risk-of-bias tool for randomised trials (RoB 2) and the risk of bias in nonrandomised studies for interventions (ROBINS-I) tools were used. Due to the heterogeneity of the included papers, a meta-analysis was unable to be completed.

RESULTS

In total, 606 records were identified, with 25 meeting the inclusion criteria; 16 papers evaluated early allograft dysfunction (EAD) with some evidence for lower rates using NMP compared to SCS; 19 papers evaluated patient or graft survival, with no evidence to suggest superior outcomes with either NMP or SCS; 10 papers evaluated utilization of marginal and donor after circulatory death (DCD) grafts, with good evidence to suggest NMP is superior to SCS.

CONCLUSIONS

There is good evidence to suggest that NMP is safe and that it likely affords clinical advantages to SCS. The weight of evidence supporting NMP is growing, and this review found the strongest evidence in support of NMP to be its capacity to increase the utilization rates of marginal and DCD allografts.

Viability assessment and transplantation of fatty liver grafts using end-ischemic normothermic machine perfusion

End-ischemic viability testing by normothermic machine perfusion (NMP) represents an effective strategy to recover liver grafts having initially been discarded for liver transplantation (LT). However, its results in the setting of significant (≥30%) macrovesicular steatosis (MaS) have not been specifically assessed. Prospectively maintained databases at two high-volume LT centers in Northern Italy were searched to identify cases of end-ischemic NMP performed to test the viability of livers with MaS ≥ 30% in the period from January 2019 to January 2022. A total of 14 cases were retrieved, representing 57.9% of NMP and 5.7% of all machine perfusion procedures. Of those patients, 10 (71%) received transplants. Two patients developed primary nonfunction (PNF) and required urgent re-LT, and both were characterized by incomplete or suboptimal lactate clearance during NMP. PNF cases were also characterized by higher perfusate transaminases, lower hepatic artery and portal vein flows at 2 h, and a lack of glucose metabolism in one case. The remaining eight patients showed good liver function (Liver Graft Assessment Following Transplantation risk score, -1.9 [risk, 13.6%]; Early Allograft Failure Simplified Estimation score, -3.7 [risk, 2.6%]) and had a favorable postoperative course. Overall, NMP allowed successful transplantation of 57% of livers with moderate-to-severe MaS. Our findings suggest that prolonged observation (≥6 h) might be required for steatotic livers and that stable lactate clearance is a fundamental prerequisite for their use.

Normothermic Machine Perfusion for Declined Livers: A Strategy to Rescue Marginal Livers for Transplantation

BACKGROUND

Organ waste is a major cause of the donor liver shortage. Roughly 67% of recovered organ donors have liver utilization annually. A new technology called normothermic machine perfusion (NMP) offers a way to recover marginal and declined livers for transplant. We report interim results of the RESTORE trial (FDA investigational drug exemption trial NCT04483102) that aims to transplant NMP-treated livers that would otherwise be discarded.

STUDY DESIGN

Declined livers were screened for NMP eligibility (eg donation after circulatory death [DCD] grafts with warm ischemic time <40 minutes, donation after brain death [DBD] grafts with cold ischemic time <8 hours). Livers meeting pre-NMP eligibility criteria received NMP using the OrganOx metra device for a minimum of 4 hours. All NMP-treated livers meeting the viability criteria were transplanted to consented recipients.

RESULTS

Over 22 months, 60 declined livers from three organ procurement organizations (OPOs; 40 DCD and 20 DBD donor livers) were offered, and 22 livers (10 DCD and 12 DBD livers) met the pre-NMP eligibility. After NMP, 16 of 22 livers passed viability testing and were transplanted into needy recipients (median Model for End-Stage Liver Disease [MELD] score of 8, range 6 to 24), resulting in a 72.7% rescue rate (50% DCD, 91.7% DBD). The rate of early allograft dysfunction was 31.3%, but there were no graft-related deaths, primary nonfunction, or instances of nonanastomotic biliary strictures.

CONCLUSIONS

Interim results of the RESTORE trial suggest that a sizable number of declined livers can be reclaimed. They are safe for transplantation and can enable lower MELD patients at high risk of morbidity and mortality to receive lifesaving grafts while offering OPOs a way to allocate more livers and reduce organ waste.

How Can Machine Perfusion Change the Paradigm of Liver Transplantation for Patients with Perihilar Cholangiocarcinoma?

Perihilar cholangiocarcinomas (pCCA) are rare yet aggressive tumors originating from the bile ducts. While surgery remains the mainstay of treatment, only a minority of patients are amenable to curative resection, and the prognosis of unresectable patients is dismal. The introduction of liver transplantation (LT) after neoadjuvant chemoradiation for unresectable pCCA in 1993 represented a major breakthrough, and it has been associated with 5-year survival rates consistently >50%. Despite these encouraging results, pCCA has remained a niche indication for LT, which is most likely due to the need for stringent candidate selection and the challenges in preoperative and surgical management. Machine perfusion (MP) has recently been reintroduced as an alternative to static cold storage to improve liver preservation from extended criteria donors. Aside from being associated with superior graft preservation, MP technology allows for the safe extension of preservation time and the testing of liver viability prior to implantation, which are characteristics that may be especially useful in the setting of LT for pCCA. This review summarizes current surgical strategies for pCCA treatment, with a focus on unmet needs that have contributed to the limited spread of LT for pCCA and how MP could be used in this setting, with a particular emphasis on the possibility of expanding the donor pool and improving transplant logistics.

Sequential hypothermic and normothermic perfusion preservation and transplantation of expanded criteria donor livers

BACKGROUND

The purpose of this study was to assess the safety and feasibility of sequential hypothermic oxygenated perfusion and normothermic machine perfusion and the potential benefits of graft viability preservation and assessment before liver transplantation.

METHODS

With the Food and Drug Administration and institutional review board approval, 17 expanded criteria donor livers underwent sequential hypothermic oxygenated perfusion and normothermic machine perfusion using our institutionally developed perfusion device.

RESULTS

Expanded criteria donor livers were from older donors, donors after cardiac death, with steatosis, hypertransaminasemia, or calcified arteries. Perfusion duration ranged between 1 and 2 hours for the hypothermic oxygenated perfusion phase and between 4 and 9 hours for the normothermic machine perfusion phase. Three livers were judged to be untransplantable during normothermic machine perfusion based on perfusate lactate, bile production, and macro-appearance. One liver was not transplanted because of recipient issue after anesthesia induction and failed reallocation. Thirteen livers were transplanted, including 9 donors after cardiac death livers (donor warm ischemia time 16-25 minutes) and 4 from donors after brain death. All livers had the standardized lactate clearance >60% (perfusate lactate cleared to <4.0 mmol/L) within 3 hours of normothermic machine perfusion. Bile production rate was 0.2 to 10.7 mL/h for donors after brain death livers and 0.3 to 6.1 mL/h for donors after cardiac death livers. After transplantation, 5 cases had early allograft dysfunction (3 donors after cardiac death and 2 donors after brain death livers). No graft failure or patient death has occurred during follow-up time of 6 to 13 months. Two livers developed ischemic cholangiopathy. Compared with our previous normothermic machine perfusion study, the bile duct had fewer inflammatory cells in histology, but the post-transplant outcomes had no difference.

CONCLUSION

Sequential hypothermic oxygenated perfusion and normothermic machine perfusion preservation is safe and feasible and has the potential benefits of preserving and evaluating expanded criteria donor livers.

A Review of Machine Perfusion Strategies in Liver Transplantation

The acceptance of liver transplantation as the standard of care for end-stage liver diseases has led to a critical shortage of donor allografts. To expand the donor organ pool, many countries have liberalized the donor criteria including extended criteria donors and donation after circulatory death. These marginal livers are at a higher risk of injury when they are preserved using the standard static cold storage (SCS) preservation techniques. In recent years, research has focused on optimizing organ preservation techniques to protect these marginal livers. Machine perfusion (MP) of the expanded donor liver has witnessed considerable advancements in the last decade. Research has showed MP strategies to confer significant advantages over the SCS techniques, such as longer preservation times, viability assessment and the potential to recondition high risk allografts prior to implantation. In this review article, we address the topic of MP in liver allograft preservation, with emphasis on current trends in clinical application. We discuss the relevant clinical trials related to the techniques of hypothermic MP, normothermic MP, hypothermic oxygenated MP, and controlled oxygenated rewarming. We also discuss the potential applications of ex vivo therapeutics which may be relevant in the future to further optimize the allograft prior to transplantation.

The role of normothermic machine perfusion (NMP) in the preservation of ex-vivo liver before transplantation: A review

The discrepancy between the number of patients awaiting liver transplantation and the number of available donors has become a key issue in the transplant setting. There is a limited access to liver transplantation, as a result, it is increasingly dependent on the use of extended criteria donors (ECD) to increase the organ donor pool and address rising demand. However, there are still many unknown risks associated with the use of ECD, among which preservation before liver transplantation is important in determining whether patients would experience complications survive after liver transplantation. In contrast to traditional static cold preservation of donor livers, normothermic machine perfusion (NMP) may reduce preservation injury, improve graft viability, and potentially ex vivo assessment of graft viability before transplantation. Data seem to suggest that NMP can enhance the preservation of liver transplantation to some extent and improve the early outcome after transplantation. In this review, we provided an overview of NMP and its application in ex vivo liver preservation and pre-transplantation, and we summarized the data from current clinical trials of normothermic liver perfusion.

Abdominal Organ Preservation Solutions in the Age of Machine Perfusion

The past decade has been the foreground for a radical revolution in the field of preservation in abdominal organ transplantation. Perfusion has increasingly replaced static cold storage as the preferred and even gold standard preservation method for marginal-quality organs. Perfusion is dynamic and offers several advantages in comparison with static cold storage. These include the ability to provide a continuous supply of new metabolic substrates, clear metabolic waste products, and perform some degree of organ viability assessment before actual transplantation in the recipient. At the same time, the ongoing importance of static cold storage cannot be overlooked, in particular when it comes to logistical and technical convenience and cost, not to mention the fact that it continues to work well for the majority of transplant allografts. The present review article provides an overview of the fundamental concepts of organ preservation, providing a brief history of static cold preservation and description of the principles behind and basic components of cold preservation solutions. An evaluation of current evidence supporting the use of different preservation solutions in abdominal organ transplantation is provided. As well, the range of solutions used for machine perfusion of abdominal organs is described, as are variations in their compositions related to changing metabolic needs paralleling the raising of the temperature of the perfusate from hypothermic to normothermic range. Finally, appraisal of new preservation solutions that are on the horizon is provided.

Introducing Machine Perfusion into Routine Clinical Practice for Liver Transplantation in the United States: The Moment Has Finally Come

While adoption of machine perfusion technologies into clinical practice in the United States has been much slower than in Europe, recent changes in the transplant landscape as well as device availability following FDA approval have paved the way for rapid growth. Machine perfusion may provide one mechanism to maximize the utilization of potential donor liver grafts. Indeed, multiple studies have shown increased organ utilization with the implementation of technologies such as ex-situ normothermic machine perfusion (NMP), ex-situ hypothermic machine perfusion (HMP) and in-situ normothermic regional perfusion (NRP). The current review describes the history and development of machine perfusion utilization in the Unites States along with future directions. It also describes the differences in landscape between Europe and the United States and how this has shaped clinical application of these technologies.

Viability Criteria during Liver Ex-Situ Normothermic and Hypothermic Perfusion

With the increased use of extended-criteria donors, machine perfusion became a beneficial alternative to cold storage in preservation strategy for donor livers with the intent to expand donor pool. Both normothermic and hypothermic approach achieved good results in terms of mid- and long-term outcome in liver transplantation. Many markers and molecules have been proposed for the assessment of liver, but no definitive criteria for graft viability have been validated in large clinical trials and key parameters during perfusion still require optimization.In this review, we address the current literature of viability criteria during normothermic and hypothermic machine perfusion and discuss about future steps and evolution of these technologies.

A Review of Defatting Strategies for Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease is a huge cause of chronic liver failure around the world. This condition has become more prevalent as rates of metabolic syndrome, type 2 diabetes, and obesity have also escalated. The unfortunate outcome for many people is liver cirrhosis that warrants transplantation or being unable to receive a transplant since many livers are discarded due to high levels of steatosis. Over the past several years, however, a great deal of work has gone into understanding the pathophysiology of this disease as well as possible treatment options. This review summarizes various defatting strategies including in vitro use of pharmacologic agents, machine perfusion of extracted livers, and genomic approaches targeting specific proteins. The goal of the field is to reduce the number of necessary transplants and expand the pool of organs available for use.

Viability testing during liver preservation

PURPOSE OF REVIEW

Viability assessment is one of the main indications for machine perfusion (MP) in liver transplantation. This review summarizes the rationale, evolution and limitations of proposed viability criteria and suggests a framework for future studies.

RECENT FINDINGS

Liver viability is most frequently assessed during normothermic MP by combining parameters relative to perfusate and bile composition, vascular flows and macroscopic aspect. Assessment protocols are largely heterogeneous and have significantly evolved over time, also within the same group, reflecting the ongoing evolution of the subject. Several recent preclinical studies using discarded human livers or animal models have explored other approaches to viability assessment. During hypothermic MP, perfusate flavin mononucleotide has emerged as a promising biomarker of mitochondrial injury and function. Most studies on the subject suffer from limitations, including low numbers, lack of multicenter validation, and subjective interpretation of some viability parameters.

SUMMARY

MP adds a further element of complexity in the process of assessing the quality of a liver graft. Understanding the physiology of the parameters included in the different assessment protocols is necessary for their correct interpretation. Despite the possibility of assessing liver viability during MP, the importance of donor-recipient matching and operational variables should not be disregarded.

Machine Perfusion for Extended Criteria Donor Livers: What Challenges Remain?

Based on the renaissance of dynamic preservation techniques, extended criteria donor (ECD) livers reclaimed a valuable eligibility in the transplantable organ pool. Being more vulnerable to ischemia, ECD livers carry an increased risk of early allograft dysfunction, primary non-function and biliary complications and, hence, unveiled the limitations of static cold storage (SCS). There is growing evidence that dynamic preservation techniques-dissimilar to SCS-mitigate reperfusion injury by reconditioning organs prior transplantation and therefore represent a useful platform to assess viability. Yet, a debate is ongoing about the advantages and disadvantages of different perfusion strategies and their best possible applications for specific categories of marginal livers, including organs from donors after circulatory death (DCD) and brain death (DBD) with extended criteria, split livers and steatotic grafts. This review critically discusses the current clinical spectrum of livers from ECD donors together with the various challenges and posttransplant outcomes in the context of standard cold storage preservation. Based on this, the potential role of machine perfusion techniques is highlighted next. Finally, future perspectives focusing on how to achieve higher utilization rates of the available donor pool are highlighted.